1. Field of the Invention
The present invention relates to a method and a device for analyzing and measuring physical parameters of a layered material by thermal radiometry.
2. Description of the prior art
The technique of analyzing materials of this type by thermal radiometry, especially photo-thermal radiometry, has been the subject of recent work directed towards measuring the thickness of a coating layer.
For a detailed and recent bibliography of publications relating to this work reference may be had to "3" topical meeting on photoacoustic and photothermal spectroscopy--Paris 5-8 April 1983. Journal de Physique, Supplement to facsicle 10, C6, 1983.
The principle of this method is to observe variations in the thermal radiation emitted by the surface of a sample illuminated by a light source amplitude modulated according to a periodic law. The radiation absorbed periodically the sample is converted by it into heat and produces thermal radiation.
This principle is applied to measuring the thickness of opaque thin films, as described in particular in European patent application EP-A-0 124 224 published Nov. 7, 1984.
According to the technique described in this patent application, two laser beams, an excitation beam and an analysis beam, are focussed on the same analysis point of the sample. The excitation beam is modulated at a very high frequency, 10,000 Hz, and the analysis beam serves to detect the thermal radiation generated as a result of excitation of the sample.
Although this method can prove satisfactory in the application envisaged, it uses a complex device because of the necessity for two laser beams and the need to focus these on the analysis point.
Also, being limited to excitation by means of coherent electromagnetic radiation, it makes no provision for widespread application in an industrial environment and in the broadest possible range of situations, because of the necessarily limited number of emission wavelengths of the excitation laser that can be used and the resulting limitations on the emission band spectrum.
An object of the present invention is to alleviate the aforementioned disadvantages by employing a method and a device for analyzing and measuring parameters of a layered material by radiometry in which the analysis laser beam is dispensed with.
Another object of the present invention is the implementation of a method and a device for analyzing and measuring parameters of a layered material in which the sample to be analyzed is excited by any appropriate means given the nature of the sample to be analyzed.
Another object of the present invention is the implementaton of a method and a device for analyzing and measuring parameters other than the thickness of the coating layer of a layered material, such as absorptivity, diffusivity and the thermal resistance of the interface beween the layers.